To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. At the present, the manufacture of 20 nm node logic devices by a double patterning version of ArF immersion lithography is implemented in a mass scale. The manufacture of 14 nm node logic devices is approaching to a mass level. The ArF lithography was adopted on 65-nm node and applied to 45 nm node owing to the immersion lithography combined with a projection lens having NA in excess of 1. The double patterning technology is adopted from 32 nm node, and the mass scale manufacture of 22 nm and 14 nm node devices is implemented by this technology. The manufacture of 10 nm and 7 nm node devices by repeating double patterning twice is under study.
In reducing a line-and-space pattern, the double patterning technology using a sidewall spacer wherein a film of SiO2 or the like is formed on both sidewalls of a pattern feature by CVD is adopted. With this technology, from a resist pattern with a half pitch of 40 nm after development, lines can be formed at a half pitch of 20 nm. It is theoretically possible to form lines at a half pitch of 10 nm by repeating the sidewall spacer process twice. On the other hand, it is known prior to the adoption of the double patterning technology that the use of negative tone image in contact hole pattern formation is superior. In the critical dimension photolithography of forming an image by utilizing the optical interference of a mask pattern, black spots in principle provide a higher image contrast than white spots. The formation of a hole pattern via negative imaging using a bright mask pattern rather than a dark mask pattern combined with positive tone resist allows for use of higher contrast light. These lead to merits such as smaller critical dimension (CD) and better CD uniformity.
The negative tone resist of conventional alkaline development type is based on a crosslinking system. A problem arises that the resist swells in the developer as a result of crosslinking whereby CD uniformity is impaired. There is a need to search for a new negative imaging technique as a replacement of the conventional crosslinking system.
Non-Patent Document 1 reports hole pattern formation via image reversal by the three methods. Included are a hole forming method (1) of using a positive tone resist composition, forming a dot pattern by two exposures of double dipole of X and Y lines, forming a SiO2 film thereon by LPCVD, and reversing the dots to holes by O2-RIE, a hole forming method (2) of forming a dot pattern by the same method as above, but using a resist material adapted to turn alkali soluble and solvent insoluble on heating, coating a phenol-based overcoat film thereon, and effecting image reversal by alkaline development, thus forming a hole pattern, and a hole forming method (3) of subjecting a positive tone resist to double dipole exposures, and effecting image reversal by organic solvent development, thus forming a hole pattern.
The organic solvent development to form a negative pattern is a traditional technique. A resist composition comprising cyclized rubber is developed using an alkene such as xylene as the developer. An early chemically amplified resist composition comprising poly(t-butoxycarbonyloxystyrene) is developed with anisole as the developer to form a negative pattern. Under such background, a highlight is again put on the organic solvent development capable of forming negative tone images.
When an isolated trench pattern is formed by negative tone development, deformation of the pattern is a problem (Non-Patent Document 2). Since the film surface of an isolated trench is widely opened, a trench pattern of tapered shape is formed. The pattern of tapered shape is undesirable because it can cause a dimensional shift during dry etching following development. When an isolated trench pattern is formed by alkaline development of a positive tone resist, such pattern deformation does not occur. When an isolated line pattern is formed by alkaline development of a positive tone resist, such pattern deformation does not occur although the situation immediately before development is the same as in the case of formation of an isolated trench pattern by organic solvent development.
Because of deprotection reaction during post-exposure bake (PEB) and evaporation of an olefin compound resulting from deprotection from the resist film, the resist film in the exposed region is shrunk. In the case of positive tone pattern formation by alkaline development, a portion of the resist film where no deprotection takes place, that is, unshrunk film is left after development. In contrast, in the case of negative tone pattern formation by organic solvent development, the shrunk film is left after development. Since the shrunk film is deformed due to internal stress applied, the pattern after development is also deformed.
Patent Document 1 discloses a chemically amplified negative tone resist material of crosslinking type and a process involving PEB in a high-humidity atmosphere. The process is effective for suppressing generation of defects bridging between lines. With respect to chemically amplified positive tone resist material, Patent Document 2 describes that PEB in a low-humidity atmosphere is better in CD uniformity. In the case of positive tone resist material based on a polymer having an acetal protective group, deprotection reaction does not take place during PEB in a low-humidity environment. Thus PEB in a moderate humidity environment is preferred. Patent Document 3 proposes a system for performing PEB under control of humidity.